Hi,
first of all I would like to know what equipment and knowledge about hardware you have.

Do you own a multimeter and know how to measure voltages and resistance?
Which JTAG cable do you have?
Did you try our flashtool? I think it is good for finding the correct JTAG pins.

First you should check which pins are GND and VCC.

Then we measure the voltage on all other pins.
Normally TCK, TMS, TDI have a pullup to VCC and DBGRQ a pulldown. You should see the resistors near the connector or near the CPU.

Then we try to find output signals DBGACK and DBGRQ. You could try if a pin goes to high if you touch all of the other pins with a 100 ohm pullup.
DBGRQ is at low level. In response to DBGRQ DBGACK will turn from low to high.

The SL3516 only has implemented a JTAG debug interface but no boundary scan.
I don't know if the Keil ulink2 will support the Cortina CPU.

Our flashtool only supports an LPT wiggler based or FTDI FT232R USB adapter. From another thread I guess you own such an adapter which may be used for this.
In the verbose mode you get some important information for checking what is happening on the pins. If 0ffff is read TDO sticks at high and if you get 0 it is at low level.
For reading the JTAG ID TDI is not required. TCK, TMS, TDO is sufficient.

The JTAG bypass Test seems to return "0x5555aaaa" on TDO which is the same pattern as sent by the tool.
The length of the USB cable is not critical. For me it looks like your JTAG connection is incorrect.

You get "Short plug detected" when the pattern sent on TDO is received on TDI without the 1 bit delay (0xaaab5554) you normally see on a JTAG interface working correctly.